A217613 Absolute value of difference between the n-th "emirpimes" A097393(n) and its reversal.

36, 36, 54, 45, 36, 27, 36, 27, 54, 45, 396, 99, 198, 792, 198, 396, 693, 792, 792, 594, 693, 198, 396, 594, 99, 297, 99, 396, 297, 693, 99, 99, 594, 198, 297, 396, 594, 198, 594, 198, 198, 198, 99, 495, 99, 99, 297, 99, 297, 297, 396, 99, 198, 297

Offset

1,1

Comments

An emirpimes ("semiprime" spelled backwards) is a semiprime whose (base 10) reversal is a different semiprime. The first such number is 15, because 15 reversed is 51 and both 15 and 51 are semiprimes (i.e., 15 = 3*5 and 51 = 3*17). Because of the decimal base, each value must be a multiple of 9.

Links

Table of n, a(n) for n=1..54.

Post, Jonathan Vos, Emirpimes. From MathWorld--A Wolfram Web Resource, created by Eric W. Weisstein.

Formula

a(n) = |A097393(n) - R(A097393(n))| = |A097393(n) - A004086(A097393(n))|.

Example

a(1) = absolute value of first emirpimes versus its reversal = |15 - 51| = |-36| = 36.
a(2) = |26 - 62| = |-36| = 36.
a(3) = |39 - 93| = |-54| = 54.
a(4) = |49 - 94| = |-45| = 45.

Mathematica

Abs[#-IntegerReverse[#]]&/@Select[Range[800], !PalindromeQ[#]&&PrimeOmega[ #] == PrimeOmega[IntegerReverse[#]]==2&] (* Harvey P. Dale, Mar 11 2023 *)

Crossrefs

Cf. A001358, A004086, A097393.

Sequence in context: A063045 A255425 A126355 * A247898 A124511 A372712

Adjacent sequences: A217610 A217611 A217612 * A217614 A217615 A217616

Keyword

nonn,base,easy

Author

Jonathan Vos Post, Oct 08 2012

Status

approved